Turfgrass IPM Advisory
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Turfgrass IPM Advisory Seasonal Turfgrass Pest Update, Utah State University Extension, Winter 2016 Turfgrass Management At this time of year, your thoughts may be turning to the potential effects of winter conditions on your turf. “Winterkill” is the general term describing turfAugust loss 28, that 2008 Volumemay VII occur as a result of winter conditions. This issue will discuss the actual causes of winterkill and how they may be prevented. News/What to Watch For During winter, most turfgrass diseases and insects are relatively inactive. However, one disease complex, the snow molds, may be at work despite current low temperatures. Focus on: Winterkill When turfgrasses die over the winter months, Dessication it may generally be described as “winterkill” (Figs. 1 and 2). The term covers During the winter when turfgrass plants are a multitude of actual causes of turfgrass dormant or semi-dormant, drying of the death in the winter, which may include snow leaves or plants (dessication) may cause mold, low temperatures, ice sheets, death. Dessication is typically only a factor dessication and crown hydration. on elevated or extremely exposed or windy sites, and areas where surface runoff is rapid. Crown Hydration Crown hydration is of most concern during the warmer days of late winter or early spring when there is the potential for a day or two of warm daytime temperatures followed by a hard freeze. Turfgrass plants may start to take up water as temperatures warm and then re-freeze rapidly. As a result, ice crystals may form in the crown of the plant, rupturing cells and causing death. Of the commonly-used cool-season turfgrass species, annual bluegrass and creeping bentgrass are most susceptible to crown hydration problems, though annual bluegrass Figure 1. Winterkill symptoms in turfgrass. is the more susceptible of the two because it emerges from dormancy earlier. Low-Temperature Kill Different turfgrass species are naturally more or less hardy in cold temperatures. In addition, the rates of freezing and thawing, the number of times frozen, and post-thawing treatment of the turf also affect low- temperature injury to grasses. Of greater concern than air temperature for low- temperature kill of turf is soil temperature, since the crowns of the plants reside within the soil. Figure 2. Winterkill on a golf course putting Ice Sheets green exacerbated by cross-country skiing. Ice sheets may be identified as the cause of winterkill in turf. However, it is more often the cycle of crown hydration and refreezing that actually kills turf. This is an understandable mistake, since ice sheets may be created as snow melts and refreezes and they are very visible. Oftentimes, ice sheets will occur in low-lying or poorly drained areas where crown hydration may be facilitated because of the standing water. The damage closely aligns with the location of the ice Figure 3. Areas prone to collecting water may sheet, causing confusion as to the actual form ice sheets. cause of death (Fig. 3). Recovery from Winterkill Low-Temperature Turfgrass Species Hardiness Confirmation of winterkill is necessary before going to the trouble and expense of Excellent Rough bluegrass reestablishment. If you suspect winterkill, take samples of the damaged area and place Creeping bentgrass them in a warm area to see if the turf greens Good Kentucky bluegrass up. Allow two weeks of recovery time before deciding on reestablishment practices. Colonial bentgrass If reestablishment is indeed warranted, Medium Annual bluegrass seeding or sodding may be necessary to facilitate recovery. Well-defined areas of Tall fescue damage may be stripped of dead turf and re- sodded. Areas of more scattered damage Red fescue may be more easily reestablished by seeding. Poor Perennial ryegrass It will also be critical to divert traffic from newly seeded or sodded areas, and to provide light fertilizer applications to stimulate growth. -Adapted from Michigan State University’s Fact Appropriate irrigation during the Sheet Winterkill of Turfgrass (E0019TURF) by reestablishment period will also ensure that Dr. Kevin Frank the seedbed or sod stays moist. Turfgrass Entomology 101 Insects are arguably the most successful life form specialized on plants that humans commonly on the planet in terms of diversity. Four out of grow. These species are considered pests—one every five organisms on Earth is an insect, and as type of insect herbivore that turfgrass is no individuals, they collectively outweigh every other stranger to. life form on the planet! Insects have been found in nearly every ecosystem, including glaciers and Turfgrass insect pests come in many shapes and even the ocean. Given this huge diversity and sizes—they can be beetles, bugs, or even moths ability to fill almost any habitat niche, it is not and flies. When we think of a beetle, we usually surprising that insects play a huge role in human think of the adult stage—a hard-bodied, six-legged life. In fact, turfgrass areas are home to many creature with a head, thorax, and abdomen types of insects—some are pests, but others are (Figure 4). However, it’s often the juvenile stages beneficial predators, and most are just minding of insects—commonly known as larvae, grubs, or their own business. caterpillars—that are pests in turf. These are the juvenile stages of insects with a complete Insects are animals in the phylum Arthropoda, metamorphosis life cycle (egg, larva, pupa, adult). meaning they have a hardened external skeleton In general, juvenile stages exist to feed and grow, and jointed appendages. Within Arthropoda, while adults exist to disperse and reproduce. Just insects are classified as hexapods, or as having six as human teenagers have seemingly bottomless legs. This classification differentiates insects from stomachs, juvenile insects have similarly voracious other arthropods, such as spiders (Arachnida), appetites. This is why the grub of a beetle or the which have eight legs, or millipedes and caterpillar of a moth is the stage we often think of centipedes (Myriapoda), which, as their name as a pest—because it is the stage that is feeding in indicates, have myriad (many) legs. order to continue development into adulthood. It’s easy to dismiss insects as annoying or Some groups of insects go through gradual, or problematic when you are dealing with them incomplete, metamorphosis, where juveniles purely in a pest management context. Considering appear as smaller, wingless versions of adults and why insects are so often pests, being able to perform similar biological functions (except for distinguish damage caused by different pests, and reproduction). Often both adults and juveniles of being able to differentiate between pests and these insects may be considered pests. beneficial arthropods dwelling in turfgrass are all important steps to bringing a holistic and sustainable viewpoint to turfgrass management. Why are insects so often pests? The vast majority of insects are herbivorous, meaning they feed on plants. Some of these insects have evolved right along with plants we have grown for food and ornamentals. Not only are these plants highly nutritious by nature (otherwise, why would humans grow them?), but management practices like irrigation and fertilization make them even more so, and they are grown as monocultures over large areas of Figure 4. Diagram of typical beetle morphology, with fiddler land. This is a recipe for a feast for insect beetle as an example species, showing the head, thorax, and herbivores, and many species have become abdominal segmentation that is common to all insects. Turfgrass Entomology 101 (cont’d) Common turf pests and their damage Turfgrass is grown widely in the Intermountain West, making the region an ideal locale for many insect herbivores that have evolved along with grasses that humans have cultivated for turf use. Common turfgrass insect pests in the region include billbugs (Figure 5), white grubs (Figure 6), sod webworms (Figure 7), and chinch bugs (Figure 8), each with their own unique biology (refer to figure captions for a physical description of the pest). Often, when the pest itself is hard to find, the damage it leaves behind can be a good identifier of its creator. Thus, it is important to know how to not only recognize the pest itself, but also its damage. Figure 6. A white grub is the larva of a beetle in the scarab family (Scarabaeidae). White grubs are c-shaped with three distinct pairs of legs. (Photo by David Cappaert, Michigan State University, bugwood.org). White Grubs. The name “white grub” refers to the larvae of several species of beetle in the scarab family. Common scarab adults in turfgrass include Japanese beetles (Figure 11), May-June beetles, masked chafers, and black turfgrass ataenius. The larvae of these beetles damage turfgrass by chewing on the roots near the soil surface or just beneath the thatch layer, sometimes entirely severing roots. Early signs of damage include wilting and yellowing. In late summer when grubs are nearly fully developed, brown patches will begin to appear. Contrary to billbugs, white grubs Figure 5. Three species of billbug are commonly found in the do not feed on the crown of the turf, meaning that Intermountain West (clockwise from left): bluegrass billbug, hunting billbug, and Rocky Mountain billbug. Billbugs are a turf can survive damage even if the roots are type of beetle in the weevil family (Curculionidae). Adults have completely severed. Because of this, and because elbowed antennae, long snouts, and hard wing covers and they do not feed within stems, turf damaged by range in size from 6-12mm. white grubs does not pull away as easily as turf Billbugs. Billbugs are a type of beetle called a damaged by billbugs. Healthy turfgrass can mask weevil. Billbug damage is one of the most the presence of white grubs when infestations are commonly misdiagnosed problems in turfgrass light.